Not Applicable
Not Applicable
Not Applicable
1. Field of the Invention
The present invention relates to a smoke generator.
Smoke generators typically used for the entertainment, including the lighting, industry, are well known and our Patent Application No PCT/GB91/02170 is an example.
2. Description of the Related Art
The entertainment industry requires for some purposes a nontoxic dense fogging which is produced by a low density mist. Of prime importance in the production of this mist is the use of a fluid characterised by low vapour pressure and a natural lack of absorption in air. Fluids which meet these characteristics are difficult to use because oxide residues produced during the smoke generation process lead to fouling of the generator conduits, particularly those within heat exchangers used in such generators. To clean these conduits it is common to split the generator which may be in a cast form. GB Patent Publication No 2 299 005 A (Dragerwerk AG) mentions the case where fluid is continuously vaporised which is conventional. The drawback of continuous flow where a low mass heating tube is concerned is that the flow regime in forced convection is very complex and random resulting in hot spots and uncontrollable and undesirable conditions. The xe2x80x2005A patent application seeks to overcome this but clogging may still occur.
Thus a smoke generator according to the invention comprises a smoke fluid supply means, a conduit in a heat exchanger connected to the supply means, the supply means being arranged to force the smoke fluid through the exchanger to a smoke outlet, wherein the heat exchanger comprises a length of electrically conductive tubing, with electrical connections spaced along the length arranged so that an electrical current may be passed along the tubing, the electrical resistance of the tubing being such that heat is generated along the tubing by the passage of electricity along the length, wherein a temperature sensor is arranged to sense the tube temperature and wherein control means is connected to the sensor and is so arranged to control an electrical supply to the electrical connections, said control means including means to cycle the electrical supply so that the power is switched on and off at a rate to allow residual fluid in the tubing to boil off.
The provision of tubing and the associated heating arrangement avoid cleaning problems.
Preferably the tubing is made of stainless steel which may be covered with a suitable insulating material such as glass fibre. The temperature sensor may function by checking the resistance of the tubing.
The control means is preferably arranged to raise the heat of the tubing to about 300xc2x0 C. and then switch off the supply to the connections and then to switch on the supply again with a cycle time of about 5 seconds. This ensures that without the introduction of further fluid any resident fluid within the tubing is boiled off. Further fluid in a small quantity suitably about 5% of the tubing volume from the supply means may then be supplied to the tubing at a suitable time preferably as the tubing temperature falls. In the preferred embodiment the control means is arranged to repeat the cycle of raising the temperature of the tubing and allowing it to fall. The provision of a one way valve at the upstream end of the tubing (that is the end toward the supply means and away from the outlet) ensures that as the fluid expands to vapour in the tubing it is ejected from the outlet without the requirement of a pump or inlet pressure as is usual. The tubing is preferably coiled for space reduction.